The Hagerman Horse

art poster featuring sketch of the Hagerman Horse as if alive
The Hagerman Horse sips water as preditors draw near.
The star of Hagerman is its horse, Equus simplicidens. Over 200 individuals have been pulled from the Hagerman Horse Quarry. These horses include adults and foals and occur in two distinct concentrations (bone beds). One of these is thought to be attritional. That means the horse bones may have accumulated along a waterway over time. For the other accumulation, weathering of bone is low and there is little evidence of carnivore damage, suggesting a quick burial. Paleontologists think these horses died along a dried riverbank during a major drought and were quickly covered with sediment once the rains returned. However they died, these horses provide information on their morphology, which tells us about their diet and locomotion, and their social structure. Their presence also tells us something about the environment. Hagerman must have had some extensive grasslands to sustain herds of horses.

These horses are also important for understanding horse evolution. Modern horses (and zebras) and all fossil horses of the genus Equus have a single hoof, but horses have been around for 55 million years (for perspective, the dinosaurs went extinct 65 million years ago) and the ancient ancestors of today's equids had a few extra toes. The modern grassland biome first appeared during the Miocene (the epoch prior to the Pliocene) and this change of the landscape triggered a response in the horse: a reduction in toes meant a gain in speed and endurance on the open plains. Running is a good technique to get away from pursuit predators like wolves and cheetahs.

Hagerman's horse was very modern-like, and in some ways resembled that of the Grevy's zebra. Genetic data tells us that it probably gave rise to other now-extinct horses in Asia, but that it is not the ancestor of any living horses. Horses evolved here in North America, but eventually went extinct here while their descendants flourished in Eurasia and Africa. Horses were later reintroduced in North America by European settlers.

The horses alone make Hagerman an important fossil site, but the other animals also play an important role. Major migration events between North and South America and across the Bering Land Bridge into Eurasia and Africa are evident. The horse travelled to Eurasia where it continued to evolve and branch off into the species of horse, zebra, and donkey that we know today. Hagerman shares fossil animals like the bear Agriotherium and the big cats Homotherium and Megantereon with Eurasia and Africa. Ancestors of the South American peccary, llama, Brazilian giant otter and grison, and the camel of Asia, were also present at Hagerman. These migrations tell us of a changing climate and landscape, one of sea level drops that exposed land bridges, encouraging migration events, and of mountain ranges that formed to keep others in (or out) and altered weather patterns. These animals show how one must adapt, move, or go extinct in the face of a changing climate. How will we respond to climate change?

Last updated: August 16, 2019

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